This is an improved process for separating carbon dioxide from hydrocarbons in a fluid mixture using a semi-permeable membrane. In particular, this process involves condensation of hydrocarbon liquids from the fluid in contact with the membrane.
Numerous references exist which describe various processes for separating gases by means of semi-permeable membranes. U.S. Pat. No. 3,415,038 described a method for separating a first gas from a gaseous mixture using a thin, dry, asymmetric cellulose acetate membrane. U.S. Pat. Nos. 3,842,515, 4,080,744, 4,080,743 and 4,127,625 describe other techniques for drying a water-wet membrane to be used in gas separation. U.S. Pat. No. 4,130,403 teaches the separation of CO.sub.2 from a natural gas stream by means of a dry cellulose ester membrane. U.S Pat. No. 4,374,657 discloses the separation of acid gases from gaseous hydrocarbon mixtures substantially free of methane by use of membranes. U.S. Pat. No. 3,616,928 describes vertical orientation of hollow fiber membrane devices to promote drainage of condensed liquid hydrocarbons during separation of hydrogen from gas mixtures.
The spiral membranes employed in the prior art for separation of carbon dioxide from light hydrocarbons are generally not suited to handling liquids. Many membrane compositions, such as those in U.S. Pat. No. 4,230,463, are deleteriously affected by liquid hydrocarbons. Heretofore, it has generally been thought that condensible hydrocarbons should be first separated from the carbon dioxide-containing gas mixture prior to bringing it in contact with the membrane.